1. Field of the Invention
The invention is related to threaded tubular joints usable in oil and gas well drilling and production, such as tubing, casing, line pipe, and drill pipe, commonly known collectively as oilfield tubular goods. More particularly, the invention relates to a seal for tubular joints for connecting male (pin) and female(box) members.
2. Description of the Related Art
Threaded tubular connections are used for joining segments of conduits end-to-end to form a continuous conduit for transporting fluid under pressure. Oilfield tubular goods generally use such threaded connections for connecting adjacent sections of conduit or pipe. Examples of such threaded end connections designed for use on oilfield tubular goods are disclosed in U.S. Pat. Nos. 2,239,942; 2,992,019; 3,359,013; RE 30,647; and RE 34,467, all of which are assigned to the assignee of this invention.
In U.S. Pat. No. RE 30,647 issued to Blose, a particular thread form or structure is disclosed for a tubular connection that provides an unusually strong joint while controlling the stress and strain in connected xe2x80x9cpinxe2x80x9d (male thread) and xe2x80x9cboxxe2x80x9d (female thread) members to within acceptable levels. The pin member has at least one generally dovetail-shaped external thread whose width increases in one direction along the pin, while the box member has at least one matching generally dovetail-shaped internal thread whose width increases in the other direction. The mating set of helical threads provide a wedge-like engagement of opposing pin and box thread flanks that limit the extent of relative rotation between the pin and box members, and define a forcible make-up condition that completes the connection. In this thread structure, the angles of the flank shoulder, as well as the thread width, can be used to control the stress and strain preload conditions induced in the pin and box members for a given make-up torque. Thus, by tailoring the thread structure to a particular application or use, the tubular connection or joint is limited only by the properties of the materials selected.
As shown in FIG. 1, a prior art tubular connection 10 includes a pin member 11 and a box member 12. Box member 12 has a tapered, internal, generally dovetail-shaped thread structure 14 formed thereon which is adapted for engaging complementary tapered, external, generally dovetail-shaped thread structure 15 formed on pin member 11 to mechanically secure the box 12 and pin 11 members in a releasable manner.
Internal thread 14 on the box member 12 has stab flanks 18, load flanks 16, roots 20, and crests 24. The thread 14 increases in width progressively at a uniform rate in one direction over substantially the entire helical length of thread 14. External thread 15 of pin member 11 has stab flanks 19, load flanks 17, roots 21, and crests 25. The thread 15 increases in width progressively at a uniform rate in the other direction over substantially the entire helical length of thread 15. The oppositely increasing thread widths and the taper of threads 14 and 15, cause the complementary roots and crests of the respective threads 14 and 15 to move into engagement during make-up of the connection 10 in conjunction with the moving of complementary stab and load flanks into engagement upon make-up of the connection.
The pin member 11 or the box member 12 defines the longitudinal axis 13 of the made-up connection 10. The roots and crests of the box and pin members are flat and parallel to the longitudinal axis of the connection and have sufficient width to prevent any permanent deformation of the threads when the connection is made up.
An important part of any connection is a seal for keeping the conduit fluid pressure-tight at the connections. Typically connections will be designed to include metal-to-metal seals therein. Metal-to-metal seals have the advantage of not requiring gaskets or other additional sealing devices, which would typically have to be replaced periodically as the connections are coupled and uncoupled. Metal seals are created when contact pressure between two metal surfaces exceeds the fluid pressure to be sealed. Typically the contact pressures are created during make up of the connection.
More recently, oilfield tubular goods have been developed which can be radially expanded from their initial diameters after being installed for the intended application. See for example, R. D. Mack et al, How in situ expansion affects casing and tubing properties, World Oil, July 1999, Gulf Publishing Co., Houston, Tex., for a description of radially expanding oilfield tubular goods. Radially expandable tubular goods have particular application as casing in oil and gas producing wells. It has been difficult to seal radially expandable tubular connections using metal-to-metal seals known in the art.
The invention is a seal for a radially expansible conduit connection or coupling. The seal includes a first sealing surface disposed proximal to an end of a male portion of the connection, and includes a corresponding second sealing surface disposed proximal to an end of a female portion of the connection. The first and said second sealing surfaces are substantially opposite each other upon connection of the male and female portions. The seal includes a first clearance surface proximal to the first sealing surface on the make portion and a includes a second clearance surface proximal to the second sealing surface on the female portion. The first and second clearance surfaces are substantially opposite each other upon connection of the male and female portions. The first and second clearance surfaces, and the first and second sealing surfaces each have a diameter such that prior to radial expansion, the clearance surfaces do not contact each other. Upon radial expansion of the male portion and female portion after coupling together thereof, the clearance surfaces remain out of contact and the sealing surfaces contact each other so as to develop a contact pressure.
In one embodiment, the clearance between the sealing surfaces prior to radial expansion of the connection is about 30 to 50 percent of the amount of radial expansion.
In one embodiment, the clearance between the clearance surfaces prior to radial expansion is about 50 to 55 percent of the amount of radial expansion.
In another embodiment, the sealing surfaces are in interference fit prior to radial expansion of the connection. After the radial expansion, the contact pressure between the sealing surfaces is increased.
In one embodiment, the coupling is a threaded coupling including mating threads on the male and female portions of the coupling. The clearance surface on the male portion is proximal to the thread end, and the clearance surface on the female portion is proximal to the thread start in the threaded coupling embodiment.